As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. One of the secondary batteries is a lithium secondary battery having high energy density, high operation voltage, and excellent storage and service life characteristics, which is now widely used as an energy source for various electronic products as well as various kinds of mobile devices.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery can be heated or explode due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) for effectively controlling the abnormality of the battery, such as overcharge, is mounted in the lithium secondary battery while the PCM is connected to a battery cell of the lithium secondary battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery to prevent the explosion or the overheating of the battery, the leakage of liquid from the battery, and the degradation of the charge and discharge characteristics of the battery, and to suppress the lowering of the electrical efficiency of the battery and the abnormal physicochemical behavior of the battery, thereby eliminating dangerous factors from the battery and increasing the service life of the battery.
Generally, the PCM is connected to the battery cell via a conductive material, such as a nickel plate, by welding or soldering. Specifically, the nickel plate is connected to electrode taps of the PCM by welding or soldering, and then the nickel plate is connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell so as to manufacture a battery pack.
In this case, several welding or soldering processes are needed to construct the battery pack, and the welding or soldering processes must be carried out with high precision because the size of the secondary battery is small. As a result, a possibility of defect is high. Furthermore, the addition of the welding or soldering processes increases the manufacturing costs of the battery pack.
Consequently, a method of assembling the PCM to the battery cell without spot welding or soldering is highly required.